Back in late 2017 i got feedback from product management that there had been discussions about adding a connector as other customers were interested but there was no defined timeline (just possibly 218 and that it would be via the Marketplace).

Does anyone know is this something still on the cards to be developed (or even via Zapier although i don't see Service Now on there currently)?

I'd bet you could use Automation as an intermediary between ISM and ServiceNow. If you need a direct integration for some reason you could certainly pitch the idea on the Ideas portal, but I think this connector might be the solution you had heard about.